1. Field of the Invention
The invention relates to a method for long seeking control, and more particularly, to a method for long seeking control employing adaptive control to a sled actuator by referring to the remaining tracks information indicating a number of tracks to be crossed, and the movement information of the sled actuator.
2. Description of the Prior Art
Pickup head control is important in an optical disc device. Control on radial movement includes static tracking, short seeking, and long seeking (also known as long jumping). Some methods and related system structures of long seeking are disclosed in Taiwan Published Patent No.479248, No.514893 and U.S. Pat. No. 6,606,283 “Long seeking method used in an optical disc drive”, etc.
Various approaches for long seeking have been proposed. For example, (1) using a stepping motor where the position of a pickup head could be determined according to a signal provided by the stepping motor, and the operating of a long seeking control is done according to the position of the pickup head, (2) controlling the pickup head by an open loop (that is, without feedback control), (3) generating a velocity profile according to the number of tracks remained to be crossed, receiving velocity information of the pickup head according to tracking signals, and controlling the pickup head by comparing the velocity profile and the received velocity information in manner of velocity feedback.
The first approach requires a stepping motor, which is more expensive than a sled actuator which only requires direct current (DC) to control. Therefore the first method is less desirable. As for the second approach, since the electrical/mechanical variances between different optical disc drives generally exist, an open loop control is generally not precise enough as required. Therefore, the third method is comparatively more preferable.
FIG. 1 illustrates a block diagram of a conventional optical disc drive 100 for accessing (that is, reading and/or writing) information on an optical disc 120. The optical disc drive 100 includes a spindle motor 110, a sled actuator 130, and a pickup head 140. The pickup head 140 is movably installed on the sled actuator 130 for accessing data on the optical disc 120. An object lens 150 is installed on the pickup head 140 for guiding a laser beam generated by the pickup head 140 toward the optical disc 120. The sled actuator 130 carries the pickup head 140 for radial movement along a direction parallel to the surface of the optical disc 120. In general, it is called long seeking when the pickup head moves over several thousand tracks (for example, 20,000 tracks for CD or 30,000 for DVD).
FIG. 2 illustrates a long seeking control system 200 of the optical disc drive 100. The velocity profile is predetermined to indicate the relation between the desired pickup head velocity (v) and the remaining tracks (t). The number of remaining tracks is the number of tracks remained to be crossed in the long seeking operation, and therefore equal to the distance between the current position (where the pickup head currently located) and the destination position. First, the number of remaining tracks is provided, and then a controller 210 generates a driving voltage according to the velocity profile and the velocity information of the sled actuator 130 to control the movement of the sled actuator 130 (and also the pickup head 140 contained therein). A velocity sensor 220 provides the velocity information of the pickup head 140 according to the tracking signals generated during the movement of the pickup head 140.
Ideally, when the numbers of remaining tracks are the same, each optical disc drive incorporating the same controller should be able to drive the pickup head to move in the same velocity. However, this is not the case because the optical disc drives generally vary in their mechanical/electrical characteristics. For example, the friction inside each optical disc drive may be different. Also, there is a friction difference between situations when the sled actuator moves in the inner radius of the optical disc or in the outer radius of the optical disc. Therefore, it is not practical to expect that a fixed velocity profile would perfectly fit all situations in all optical disc drives. Moreover in the prior art, feedback control depends on the velocity information (or sometimes also depends on the number of remaining tracks), which is also not precise enough for long seeking control.